I recently replaced the PET tape on my heated bed (TAZ 4) and while attempting to level it, I noticed that the left side of the bed sat lower then the right side when compared to the nozzle. As the nozzle moved right, it would get closer to the build plate (like it was going up a hill). I pulled the level out and the bed is level, just not with the nozzle. BTW, every time I adjust the left side using the paper method, the right side is completely touching the nozzle. Any ideas?
Make sure your X axis smooth rods are parallel to the aluminium Y axis bed plate by measuring from the lower smooth rod to the AL plate on each side. If the measurements are different, correct them by slowly turning one of the Z drive motors while the printer is powered off.
Once that is done, go back to the glass and use the corner adjusters to get a consistent gap between the glass and the nozzle.